A 99% cache-hit ratio can be a lie

A 99% cache-hit ratio can be a lie
A Dublin recipe site bragged about a 99% cache-hit ratio while their Google rankings tanked on slow mobile loads. Something didn't add up.
The myth: high cache-hit ratio means fast site. The reality: their hit ratio counted tiny CSS and icon files, which dominated request volume. The HTML document, the thing users wait for, was a 100% miss on a slow origin.
What we changed: we segmented the ratio by content type. HTML showed 0% caching. We enabled edge caching for the document with stale-while-revalidate and a cookie-aware key.
Result: HTML cache-hit jumped to 88%, Dublin TTFB fell from 600ms to 40ms, and mobile rankings recovered within weeks.
An aggregate hit ratio hides the file that actually matters. Slice it by type.
The number that mattered: 40ms HTML TTFB, down from 600.